1. Field of the Invention
The present invention relates to a device for fixing or fastening an optical unit of a laser gyrometer to an actuating mechanism.
The present invention can be applied both to single-axis gyrometers in which the optical cavities extend in one and the same plane as well as to triaxial gyrometers in which the optical cavities extend in three dimensions.
2. Dicussion of the Background
In general, it is known that the optical units used in laser gyrometers are made out of materials having very low coefficients of expansion such as quartz or Zerodur. Indeed, these optical units comprise resonant optical cavities made by very high-precision machining. The dimensions of these cavities must remain constant whatever the environment in which they are placed (especially in a very wide range of temperature).
Furthermore, to avoid disturbances through flows within the cavities, the optical unit must have high thermal homogeneity so as to prevent the presence of high thermal gradients as far as possible.
The actuating mechanism used to drive the unit in an alternating rotational motion is usually made of a metal with high properties of elasticity but with a coefficient of expansion that is not negligible.
Given the nature and the properties of the materials used, the fastening of the optical unit to its actuating mechanism raises many problems.
First of all, the hardness of the unit, its fragility (frangibility) and the fact that it is poorly machinable rule out most standard fastening means, given that these means generally induce defects of mechanical and thermal homogeneity in the unit. These defects run counter to the goals in view.
Nor is the bonding of the unit directly to an actuating ring a satisfactory solution, given the phenomena of differential expansion between the ring and the unit: This differential expansion creates shear strains at the bonding zone prompting the breakage of the link between the unit and the activating ring.
Furthermore, the relatively large surface area of contact between these two parts, which is necessary for efficient fastening, induces thermal heterogeneity within the unit.